Stabilizer for silver halide emulsions



United States Patent 3,274,002 STABILIZER FOR SILVER HALIDE EMULSIONS Vere Mafiet, New Brunswick, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Dec. 27, 1963, Ser. No. 334,033 6 Claims. (Cl. 96-109) This invention relates to photographic emulsions, and more particularly to stabilized silver halide photographic emulsions, and to a method for preparing such emulsions. Still more particularly, this invention relates to gelatino-silver halide photographic emulsions of improved speed and stability and to a method for preparing such emulsions.

It is well known that light-sensitive silver halide emulsions have a tendency to fog. Such fog may be caused in a number of different ways as, for example, by excessive ripening, prolonged storage, particularly at elevated temperature and humidity such as might be encountered in the tropics, or by prolonged development of the exposed emulsion. Fog may also be caused by exposure to certain chemicals, for example, hydrogen sulfide or other reactive sulfur compounds and also by strongly reducing compounds.

A great number of substances have been described in the literature as being effective in preventing or substantially reducing fog by stabilizing or controlling the keeping qualities of light sensitive silver halide emulsions. Although the majority of these compounds have the ability to reduce fog tendencies and to improve stability, they are deficient in that they lower the sensitivity of the emulsions and may seriously interfere with other desirable sensitometric properties, e.g., speed and contrast.

It is an object of this invention to provide a method of stabilizing silver halide emulsions against fog caused by excessive ripening. A further object is to provide a method of stabilizing silver halide emulsions against fog caused by prolonged storage, particularly at elevated temperatures and humidity. A still further object is to provide photographic elements, the silver halide emulsion of which contain stabilizing agents which do not lower the sensitivity or interfere with the desirable sensitometric properties, e.g., speed and contrast. Other objects will become apparent from the following description and examples.

The foregoing objects are attained and stable photographic s-ilver halide emulsions and emulsion layers are provided in accordance with the invention by adding to an aqueous light-sensitive emulsion a small amount of at least one pantothenic compound taken from the group consisting of the calcium salt of pantothenic acid, pantothenoyl lactone and DL-pantothenal.

The above compounds preferably are added to the emulsion after the completion of the digestion stage and prior to coating. The stabilizing compounds may be added at the same time as other various adjuvants are added, e.g., spreading agents, ant ifoaming agents, optical and non-optical sensitizers, hardening agents, etc. EX- vamples of non-optical sensitizing agents are polyoxyalkylene compounds and derivatives thereof such as those disclosed in US. Patents 2,423,549, 2,441,389, and 2,400,532 and various metal salts such as gold salts and the so-called sulfur sensitizers.

In preparing the stabilized emulsions of this invention it has been found that one or more of the above compounds may be added in amounts ranging from 0.1 to grams per mole of silver halide. The optimum amount to be added depends primarily on the type of emulsion and can readily be determined individually in each case.

The antifoggant and stabilizing .action were determined by incubation of the emulsions for one week under conditions of 65% relative humidity at F. The results were compared with initial speed, gamma and fog and are tabulated in the examples which follow below. The test exposures from which the test data were derived were carried out on an Eastman Type 1B sensitometer and unless specified in the particular example, were developed in a developer having the following composition:

Grams N-methyl-p-amino phenol hydrosulfate 0.8 Sodium sulfite (desiccated) 90.0 Hydroquinone 1.0 Borax 3.0 Potassium bromide 0.1

Water to make 1 liter.

The following examples will illustrate the invention in greater detail, but are not intended to limit this invention. In the tables the amount of the stabilizing agent is in parts of grams or grams per mole of silver halide. In these examples, the emulsions were prepared and coated in the absence of actinic radiations in amounts which would cause significant exposure of the emulsions.

Example I A high speed panchromatic gelatino-silver iodobromide emulsion digested with sulfur and gold compounds and containing about 7 mole percent silver iodide and 93 mole percent silver 'bromide was prepared in a conventional manner and divided into two equal parts, one of which was used as a control. The control was coated on a transparent film support after the usual final additions had been added prior to coating. To the other part there was added with the final additions prior to coating 0.66 gram per mole of silver halide ofthe calcium salt of pantothentic acid. Both coated samples were dried in a conventional manner. Samples of each coating were exposed in an Eastman Type 113 sensitometer and developed in the developer disclosed above for 7 minutes at 68 F. with the following results.

3 Example 11 Example I was repeated, except that DL-pantothenal was used in an amount of 3.3 grams per mole of silver halide in place of the calcium salt of pantothenic acid. The results were as follows:

Fresh 1 week, 120 F., 65% RH Relative Gamma Fog Relative Gamma Fog Speed Speed Control 1, 000 73 09 660 68 12 Sample 1, 000 76 05 770 65 07 Example Ill Example I was repeated, except that DL-pantothenoyl la'ctone in an amount of 1.6 grams per mole of silver halide was used in place of pantothenic acid calcium salt.

Fresh 1 week, 110 F., 65% RH Relative Gamma Fog Relative Gamma Fog Speed Speed Control 1, 000 73 09 660 68 12 Sample 1, 100 74 05 660 72 08 Example IV Example I was repeated except that 55 grams of glucono delta lactone per mole of silver halide was added just prior to digestion and no pantothenic acid derivative was added as a final addition.

A high-speed gelatino-silver iodobrornide emulsion of the X-ray type containing approximately 1.5 mole percent silver iodide and 98.5 mole percent silver bromide was prepared in the usual manner. The emulsion was divided into two equal parts which were given a norm-a1 digestion. One part, Without further treatment, was coated on a suitable film support and dried. To the other part, the calcium salt of pantothenic acid was added just before coating in an amount of 0.17 gram per mole of silver halide. Samples of both the control and the one containing the pantothenic acid derivative were then given an X-ray' screen exposure of 15 milliampereseconds, 71 kilovolts potential, at a distance of 55 inches through a l-millimeter aluminum filter using an aluminum step-wedge and then were developed in a developer having the following composition:

Grams N-methyl p-aminophenol hydrosulfate 3.0 Hydroquinone i 9.0 Sodium sulfite (desiccated) 50.0 Potassium bromide 4.5 Potassium carbonate 50.0 Water to make 1.0 liter.

Development was for 5 minutes at 68 F. Results were as follows:

-It will be apparent from the foregoing examples that the stability of photographic emulsions is markedly improved, particularly in regard to fogging at elevated temperatures. It will also be apparent that the stabilizing compounds may be used in quantities varying over a wide range and that the speed and gamma characteristics are not adversely affected by the addition of the stabilizing compounds. As a matter of fact, it will be seen from the above results that the presence of one of these compounds improves the sensitivity of the emulsions in which they are incorporated.

Although the examples are directed to silver iodobromide emulsions, the invention is by no means so limited. The invention may be utilized in silver chloride, silver chlorob-romide, and silver bromide emulsions. The invention may also be used eifectively in silver halide systems having other organic colloid binders besides gelatin and also in systems containing developed silver covering power increasing agents as for example in assignees U.S. patents: Jennings, 3,063,838, dated November 13, 1962; Chambers U.S. 3,043,698, dated July 10, 1962; Chambers U.S. 3,069,267 dated December 18, 1962; Chambers U.S. 3,085,009 dated April 9', 1963; Chambers U.S. 3,085,010 dated April 19, 19 63; Chambers U.S. 3,087,818 dated April 30, 1963. Synthetic macromolecular organic waterpermeable colloids that form coherent films and may be used to prepare the silver halide emulsions are those disclosed in assignees Shacklett, U.S. Patent 2,777,872 dated January 15, 1957; Shacklett, U.S. Patent 2,830,972 dated April 15, 1958; Shaoklett, U.S. Patent 2,833,650 dated May 6, 1958 and Shaoklett, U.S. 2,834,758 dated May 13, 1958. Polyvinyl alcohol, polyvinyl acetal-s, and certain cellulosic derivatives which the prior art teaches as being useful gelatin substitutes or extenders may also be used.

The emulsions of this invention may be coated onto any suitable support to make the desired type of photographic element. Suitable supports include cellulose esters, e.g., cellulose acetate, cellulose nitrate, cellulose acetate butyrate, cellulose propionate, super polymers, e.g., nylon, polyethylene terephthalate, polyvinyl chloride, vinylidene chloride copolymers with vinyl acetals, acrylonitrile, etc.; metal sheets foils, e.g., aluminum and zinc; and paper including resin coated and baryta coated paper; as well as glass plates. Typically, the supports will carry preliminary coatings of suitable substrata to improve the adhesion of the emulsion layer to the support. 7

Another advantage of this invention is that it provides a simple and etfective process for improving the stability of photographic emulsions. The process of adding the compounds is not only simple, but the compounds are easily obtainable. Another advantage is that the method of stabilizing the emulsions can be practiced successfully by the ordinary technician and extreme care does not have to be exercised in controlling the amount of the stabilizing agent which is added. A further advantage is that the emulsion may be aged over a wide range of climatic conditions and the stabilizing compounds of the invention will still retain their eiiectiveness.

I claim:

1. A photographic layer comprising a dispersion of light-sensitive silver halide grains in a water-permeable, macromolecular organic colloid binder containing 0.1 to grams of a stabilizing agent selected from the group consisting of the calcium salt of pantothenic acid, pantothenoyl lactone and DL-pantothenal per mole of silver halide.

2. A photographic layer according to claim 1 wherein said binder is gelatin.

3. A photographic layer according to claim 1 wherein said grains are silver iodobromide gnains and said binder is gelatin.

4. A method for stabilizing an aqueous digested lightsensitive silver halide emulsion which comprises admixing therewith a stabilizing agent selected from the group consisting of the calcium salt of pantothenic acid, pantothenoyl lactone and DL-pantothenal in an amount of 6 is a gelatino-silver iodobromide emulsion.

References Cited by the Examiner UNITED STATES PATENTS 4/1953 Land 96-29 NORMAN G. TORCHlN, Primary Examiner. J. H. RAUBITSOHEK, Assistant Examiner. 

